1. Field of the Invention
The invention is directed to emergency signal displays, and more particularly to circuitry for controlling such displays.
2. Related Art
U.S. Pat. No. 3,869,639 discloses a control circuit for switching a gaseous lamp between dim and bright output in an emergency, such as line failure, using the increased impedance of a ballast capacitor.
U.S. Pat. No. 4,298,869 relates to an LED display using a combination of serially and parallely connected LEDs powered by a full-wave rectifying circuit and a smoothing circuit.
U.S. Pat. No. 4,388,615 discloses stand-by battery equipment used when the mains supply fails and is tested at regular intervals by disconnecting the mains supply.
U.S. Pat. No. 4,544,910 relates to an emergency exit sign auxiliary lamp flashing system operated from self-contained rechargeable batteries upon failure of the AC power mains and using a solid state circuit which automatically self tests the proper functioning of the system to ensure that it is serviceable in case of an emergency.
U.S. Pat. No. 4,682,147 discloses an emergency sign with a control circuit supplying power to serially-connected LEDs which are illuminated continuously during normal operation and which alternately switches the LEDs on and off during a power failure.